The present invention is an improvement over the envelope and sheet feeding apparatus disclosed in U.S. Pat. No. 3,934,868. As disclosed therein, the feeding apparatus includes three widely spaced suction cups supported on individual arms movable between an initially lowered position and a raised position where the suction planes of the suction cups are parallel to and engage the bottom exposed surface of the bottommost sheet in a stack of the same held in a top loadable stacking frame, so that the operation of the apparatus does not have to be interrupted when the supply of sheets is to be replenished. The stack of sheets preferably rests on a slightly forwardly inclined support tray which terminates short of the lower front end of the stack to leave an opening running the entire width of the stack to expose thereat the bottom sheet in the stack for engagement by one or more of the suction cups. The front end of the stack rests on a rigid support ledge so that when the bottommost sheet is pulled from the stack by the lowering of the suction cups, the weight of the stack above the same will tend to maintain this next sheet within the stacking frame. The suction applied to the suction cups is released in the lowermost position thereof where the sheet is applied to a feed or drive roller which directs the sheet to other sheet feeding apparatus.
The sheets of material in apparatus of the type described are commonly held in a neat vertical stack upon said support tray by vertical guide members. As disclosed in U.S. Pat. No. 934,868, these vertical guide members are removably and adjustably mounted upon the support tray for lateral adjustment to accommodate sheets of different width. Thus, one or more pairs of such guide members can be mounted on the support tray with the desired lateral spacing, to accommodate one or more stacks of sheets, which could be envelopes or other sheet material. The aforementioned support ledge at the front of the stacking frame formed by these guide members is generally associated with a vertical support wall which fixes the forward position of the stack of sheet material. The rear of each stack of sheet material is generally engaged by one or more vertical guide members which are adjustable upon the support plate in a longitudinal direction to accommodate sheet material of varying length. It can be appreciated that where only a few sidely spaced suction cups are utilized to engage various sheet material like envelopes oriented with their length extending longitudinally of the apparatus, so that only one suction cup will be positioned opposite the same, the position of each stack of envelopes involved for reliable withdrawal thereof by these suction cups should be centered with respect to one of the suction cups. Generally, the closure flaps of the stacked envelopes are on the bottom sides thereof. If the operator carelessly aligns the stack of envelopes so that the suction cup is substantially offset from the center line of the envelopes, the suction cup can engage the portion of the envelope where the flap is located, and overlap the same, with the result that the suction cup does not make a seal with the flap so that the suction cup slips from the envelope during the downward movement thereof from the stack. It is accordingly, another object of the invention to provide sheet feeding apparatus which reliably operates with envelopes or other sheet material of widely varying sizes and orientations, and without the necessity of the operator centering the stacks of sheet material with any suction cup.